1. Field of the Invention
The present invention relates to a method and apparatus for measuring ultraviolet protection effectiveness, and more particularly to a method and apparatus for obtaining in vitro SPF values having a high degree of correlation with SPF values measured on human skin (SPF--Sun Protection Factor: the degree of protectiveness provided by cosmetics against sunburn caused by exposure to ultraviolet radiation).
2. Description of the Related Art
SPF Values are used to indicate the effectiveness of sunscreen preparations, generally known as suncare products, in protecting the skin against sunburn caused by exposure to ultraviolet radiation. The SPF is an index to indicate the effectiveness in protecting the skin against sunburn from ultraviolet B radiation (that causes redness, flushing, or inflammation on the skin in short periods of time), and is defined as follows. EQU SPF=WITH SUNCARE PRODUCT APPLIED, UV AMOUNT NECESSARY TO CAUSE SLIGHT REDNESS (MED: MINIMUM ERYTHEMA DOSE)/WITH SUNCARE PRODUCT NOT APPLIED, UV AMOUNT NECESSARY TO CAUSE SLIGHT REDNESS (MED: MINIMUM ERYTHEMA DOSE) (1)
A suncare product with SPF 8, for example, means that with this suncare product applied on the skin, the same degree of sunburn would be caused as an unprotected skin when the protected skin was exposed to eight times as much ultraviolet B radiation as the unprotected skin.
For the measurement of SPF values, an artificial light (solar simulator), very close to sunlight, is used since with real sunlight the value can vary from season to season and from place to place. In a commonly practiced measurement method, skin protected with a suncare product and unprotected skin are exposed to the same amounts of ultraviolet radiation, and are examined the next day to determine whether sunburn (erythema) has been caused on the skin.
In the U.S., the SPF measurement procedures are specified by Federal Register OTC monograph (1978) of FDA as follows.
1. Subjects are males and females, age 18 or older, with skin types I to III*.
2. The number of subjects is 20 or more.
3. Prescribed sunscreen preparations with SPF 4 are used as the standard sample.
The quantity of sample application is 2 mg(.mu.s)/cm.sup.2.
5. The area of sample application is 20 cm.sup.2 or more.
6. The time from sample application to UV irradiation is 15 minutes or more.
7. The light source used is solar UV-B light, wavelengths 290 to 320 nm, or a solar simulator close to solar light.
8. Irradiation area is 0.5 cm.sup.2 or more.
9. Irradiation amount is increased by the same proportion, the proportion not exceeding 25%.
10. MED evaluation is made by a skilled person in the light 16 to 24 hours after the end of the irradiation.
11. SPF is calculated in accordance with a formula, using the MEDs of the panels obtained from the part with sample application and the part without sample application.